The present invention relates to a method of and system for continuously processing liquid material such as liquid foodstuff or liquid medicine using a supercritical or subcritical fluid. The xe2x80x9cprocessingxe2x80x9d hereby includes: inactivation of enzymes and spores in and sterilization of liquid foodstuffs, liquid medicines or the like; and deodorization of liquid foodstuffs. The present invention also relates to a liquid material produced by the method or system according to the present invention.
There are various kinds of foodstuffs containing enzymes there days, in which sake, beer and juice are typical examples. In general, a process of producing sake includes: first step where fermented rice is compressed and filtered to obtain shinshu (green sake); second step where this obtained green sake is sterilized by heating and then stored; third step where plural lots of stored sakes are properly mixed to determine the sake quality and the alcohol content is adjusted to the standards; and fourth step where the thus adjusted sake is again sterilized by heating and then bottled or packed. As described above, sake undergoes the heat-treatment twice in the second and fourth steps in the manufacturing process to inactivate and kill bacteria therein, whereby the sake quality is prevented from deteriorating during market circulation. A problem here is that the fresh aroma of green sake is sharply reduced by the heat-treatments. Therefore, a non-heat-treated sake, or fresh sake, preserving the fresh taste and aroma, is in great demand. To meet the demand, the fresh sake is also circulated in the market by keeping it at low temperature. Such a non-heat-treated sake, however, contains enzymes such as xcex1-amylase and protease, which deteriorate the sake quality. The increased circulation cost due to the low temperature circulation is anther problem.
As for muddled fruit drinks such as orange juice, it is necessary to inactivate pectin esterase in order to maintain the muddled state of the drink. Since pectin esterase is stable to heat, a heat-treatment for inactivating this enzyme must be conducted at high-temperature (88-99xc2x0 C., or 120xc2x0 C.). The heat-treatment at such high temperature, however, deteriorates the relish of the drink.
Regarding the above-described problems, some of the inventors of the present application proposed a method of processing liquid foodstuff containing enzymes, as disclosed in Japanese Unexamined Patent Publication No. H07-170965, where the enzymes are inactivated by contacting carbon dioxide in a supercritical state. According to this method, the liquid foodstuff containing enzymes is contained in a processing chamber, which is then sealed, and supercritical fluid of carbon dioxide is supplied into the sealed processing chamber. The temperature and pressure inside the processing chamber are kept appropriately under preset conditions, and the supercritical fluid is supplied into the chamber through a filter whereby the fluid is formed into micro-particles having diameters of about a few hundreds of micrometers or less. Thus, the supercritical fluid of carbon dioxide effectively dissolves into the liquid foodstuffs. This method not only improves the inactivating efficiency, but also is highly safe since it is only carbon dioxide that contacts the liquid foodstuff. By this method, simultaneously, microorganisms such as bacteria, yeast fungus or mold can be killed.
Also, some of the inventors of the present application proposed a continuous processing system constructed so that the inactivating and sterilizing process is carried out more effectively and with less quality deterioration (Japanese Unexamined Patent Publication No H09-206044 or corresponding U.S. Pat. No. 5,704,276). With this continuous processing system, the liquid foodstuff is continuously supplied into a processing chamber from its bottom while maintaining the inside of the chamber at preset temperature and pressure. Carbon dioxide in a supercritical state is continuously supplied into the processing chamber through a mesh filter provided at the bottom of the chamber. In the upper part of the processing chamber is located a take-out port at a level a little lower than the level of the liquid foodstuff, from which the product (or processed liquid foodstuff) is taken out. In the processing chamber, the liquid foodstuff and micro-particles of the supercritical fluid flow upwards in parallel, contacting each other, whereby the enzymes are effectively inactivated. The processing chamber also has a drainage port for draining the supercritical fluid from the chamber. The supercritical fluid taken out from the drainage port is returned to a carbon dioxide source to be used again. Since this system can continuously process a liquid foodstuff, it is suitably used in a drink or food factory where a large amount of liquid foodstuff is to be processed.
With the above-described continuous processing system, the inactivation of enzymes in or sterilization of liquid materials is efficiently carried out. The practical use of this system, however, is difficult because of the cost problem as follows.
In the above continuous processing system, the temperature of the processing chamber must be kept at or above 31.1xc2x0 C. in order to maintain the carbon dioxide in the supercritical state. Such a condition relating to temperature, however, is not preferable in view of efficient dissolution of carbon dioxide into the liquid foodstuff because carbon dioxide less dissolves into a liquid foodstuff as the temperature is higher. Hence, for obtaining an adequate inactivating and sterilizing effect, it is necessary to keep the liquid foodstuff and the supercritical fluid flowing in parallel for a considerably long time (from a few minute to a few tens of minutes, for example). Such a long processing time can only be realized by using a processing chamber of a large capacity. Also, a warming apparatus is necessary to the processing chamber to maintain the above-mentioned temperature. Another warming apparatus is necessary for moderately warming the liquid foodstuff in the course of transfer from a source to the processing chamber, because the reaction in the processing chamber is slow if the temperature of the liquid foodstuff supplied into the processing chamber is low. Thus, the continuous processing system becomes inevitably large and requires a large installation space, and the construction cost should be high.
Another problem lies with respect to the temperature of the processing chamber. Though, in the above-described system, the temperature in the processing chamber is considerably lower than the temperature for inactivating enzymes by heat, the temperature; is higher than a normal ambient temperature. It is possible therefore that the quality of the liquid foodstuff is deteriorated while the liquid foodstuff is kept at such a temperature for the process contains enzymes of high activity, and the enzymes badly affect the quality of the juice in the processing chamber before they are completely inactivated.
For solving the above-described problems, one object of the present invention is to propose a method of and system for continuously processing liquid materials with a small-sized processing chamber (or chambers) and a minimum number of warming apparatuses. The present invention also proposes a liquid material processed by such method or system.
In the above-described continuous processing system, the process of dissolving carbon dioxide into the liquid material and the process of changing the carbon dioxide into a supercritical state and maintaining the state are carried out simultaneously in the processing chamber. In contrast to that in the method or system according to the present invention the two processes are carried out separately in time and space.
Thus, in a method of continuously processing a liquid material such as liquid foodstuff with a supercritical or subcritical fluid, the process according to the present invention includes:
a) a dissolving stage where a liquefied carbon dioxide is continuously supplied into the liquid material while the liquid material is continuously supplied to dissolve the liquefied carbon dioxide into the liquid material;
b) a critical processing stage where the liquid material with the liquefied carbon dioxide dissolved therein is kept under a preset temperature-and-pressure condition so that the carbon dioxide is brought into a supercritical or subcritical state; and
c) a pressure-reducing stage where the pressure of the liquid material after passing the critical processing step is reduced rapidly to remove the carbon dioxide and the liquid material is retrieved as a product.
Also, in a system of continuously processing a liquid material with a supercritical or subcritical fluid, the system according to the present invention includes:
a) a material supply line for continuously supplying the liquid material;
b) a carbon dioxide supply line for continuously supplying a liquefied carbon dioxide;
c) a dissolving part where the liquefied carbon dioxide supplied through the carbon dioxide supply line is dissolved into the liquid material while the liquid material is continuously supplied through the material supply line;
d) a critical processing part where the liquid material taken out from the dissolving part with the liquefied carbon dioxide dissolved therein is kept under a preset temperature-and-pressure condition so that the carbon dioxide is brought into a supercritical or subcritical state; and
e) a pressure reducing part where the pressure of the liquid material after passing the critical processing part is reduced rapidly to remove the carbon dioxide and the liquid material is retrieved as a product.
The liquid material according to the present invention is characterized in that it is processed and retrieved by the method or system according to the present invention.
By the method or system according to the present invention, a liquid material such as a liquid foodstuff or liquid medicine is continuously supplied through the material supply line into the dissolving part, while a cooled and liquefied carbon dioxide is continuously supplied through the carbon dioxide supply line into the dissolving part. A mesh filter having a small mesh size may be placed at the exit of the carbon dioxide in the dissolving part. In this case, when the liquefied carbon dioxide passes through the filter, the carbon dioxide is formed into micro-particles and dissolves into the liquid material. High-speed mixers, ultrasonic generators or other devices may be used for improving the contacting efficiency of the carbon dioxide and the liquid material. It is desirable to cool the dissolving part because, as generally known, the solubility of liquefied carbon dioxide in a liquid is higher as the ambient temperature is lower. Even at a room temperature, an adequate amount of liquefied carbon dioxide dissolves into the liquid material in a short time period. The dissolving efficiency is high in winter since the ambient temperature is low.
For example, the dissolving part is constructed using a dissolving chamber, where an entrance for the liquid material from the material supply line and another entrance for the liquefied carbon dioxide from the carbon dioxide supply line are located at the bottom of the dissolving chamber, and an exit for the liquid material is located at about the level of the liquid material of the upper part of the dissolving chamber. Owing to this construction, the liquid material introduced from the bottom of the dissolving chamber flows upwards in the dissolving chamber, and the micro-particles of the liquefied carbon dioxide flow in the same direction. Thus given a large contact area, the liquefied carbon dioxide efficiently dissolves into the liquid material.
The dissolving part may be constructed using a pipe provided as the material supply line (a material supply pipe), where the liquefied carbon dioxide is made to dissolve into the liquid material by discharging the liquefied carbon dioxide into the liquid material. Such a construction is advantageous in that the system can be made smaller in size because there is no need to provide a dissolving chamber or the like.
One method of improving the efficiency of dissolving the carbon dioxide into the liquid material is that a mesh filter is placed in the material supply pipe and the liquefied carbon dioxide is made to pass through the mesh filter so that the liquefied carbon dioxide is formed into micro-particles in the liquid material. Another method is that a mixer is placed in the material supply pipe and the liquefied carbon dioxide is discharged into the liquid material at upstream of the mixer. As described above, the solubility of liquefied carbon dioxide in a liquid is higher as the ambient temperature is lower. Accordingly, it is preferable to cool the material supply pipe at the part where the filter or mixer is placed. In this case, however, it is not necessary to cool the material supply pipe to an abnormally low temperature because an adequate amount of liquefied carbon dioxide dissolves into the liquid material in a short time period even at the room temperature. Naturally, therefore, the dissolving efficiency is high in winter since the ambient temperature is low. Therefore, a considerable advantage is obtained by simply keeping the temperature of the above-mentioned part of the material supply pipe.
The liquid material in which the liquefied carbon dioxide is dissolved is then transferred from the dissolving part to the critical processing part. In the critical processing part, the liquid material with the liquefied carbon dioxide dissolved therein is kept under a preset temperature-and-pressure condition so that the carbon dioxide is brought into a supercritical or subcritical state. A preferable temperature condition is 30-80xc2x0 C., more preferably 30-50xc2x0 C., and a preferable pressure condition is 40-400 atm, more preferably 100-300 atm. Under such a condition, the liquefied carbon dioxide dissolved in the liquid material is rapidly brought into a supercritical or subcritical state. The time period for keeping the liquid material under such a condition may be as long as 1 minute or so. Therefore, even though the temperature in the critical processing part is higher than the room temperature, deterioration of the quality of liquid material due to the heat is minimized.
After being processed in the critical processing part, the liquid material is transferred to the pressure-reducing part, where the pressure of the liquid material is rapidly reduced (pressure-reducing process). Then, carbon dioxide having permeated into the enzymes swells rapidly, whereby the protein of the enzymes is destroyed and the enzymes are inactivated. Similarly, various kinds of microorganisms are also killed. The carbon dioxide in the liquid material thus turns to gas and is discharged from the liquid material. After that, the liquid material is retrieved as a product. In the above-described pressure-reducing process, it is important to regulate the pressure-reducing speed. When, for example, a pressure control valve having an orifice is used for the pressure reduction, the pressure-reducing speed should be determined so that every molecule of the liquid material passes through the orifice within 20 milliseconds, more preferably within 10 milliseconds.
Typical liquid materials which can be processed by the method or system according to the present invention are: fermented or brewed liquid foodstuffs such as green sake, beer, wine, soy sauce; juices; cooling beverages, etc. Some juices are produced from fruits such as apple, grape or orange, and other juices are produced from vegetables such as tomatoes, and the process of the present invention is generally applicable to all kinds of juices. Not only liquid foodstuffs as listed above, but also liquid medicine such as transfusion liquids, blood derivatives nutritious drinks can be processed by the method or system according to the present invention.
As described above, by the method or system according to the present invention, the process of dissolving the liquefied carbon dioxide into the liquid material and the process of bringing the carbon dioxide into a supercritical or subcritical state are separately carried out. Owing to this construction, each process is carried out with a very high efficiency, and the total processing time is greatly shortened compared to the processing time required by the conventional continuous processing method or system. Since neither the large-sized processing chamber nor the warming apparatus is necessary, the system can be designed smaller in size. In the critical processing step, the temperature can be optimized, so that a higher efficiency is obtained with respect to the inactivation of enzymes in and the sterilization of the liquid material. The time period of keeping the liquid material at high temperature is short, so that there is little or no possibility of damaging fresh aroma of the product.